Paleosols, stable carbon isotopes, and paleoenvironments of hominid evolution in the Neogene Turkana Basin, northern Kenya

The role of environmental forcing on human evolution has long interested the scientific community, and has been a major focus of paleoanthropological research towards understanding human origins. This dissertation documents the history of soil formation, and the environments represented by paleosols throughout the hominid-bearing Neogene exposures of the Turkana Basin, northern Kenya. From this database, the role of regional environmental change in early hominid habitat selection is assessed.; In the late Miocene to early Pliocene deposits of Lothagam Hill, stratigraphic changes in paleosol types indicate a response to the well documented late Miocene (Messinian, 6.7–5 Ma) global cooling event, which may have precipitated the origins of the family Hominidae (genus Orrorin or Ardipithecus). However, at present, the fossil record of hominids in the late Miocene is too fragmentary to assess these evolutionary relationships, despite the growing record for paleoenvironmental change. Paleosols and stable carbon isotope ratios from pedogenic carbonate at Kanapoi (4.3–3.9 Ma) indicate that hominids during that interval (Australopithecus anamensis ) had already begun to inhabit open savanna ecosystems. Stable carbon isotopic data, as well as paleoprecipitation estimates from the Pliocene and Pleistocene Omo Group (4.2–0.5 Ma) indicate a trend towards increasing aridity, with increasing amplitude of high frequency climatic events (ca. 10,000–100,000 yr.). This aridification was punctuated by 3 intervals of stepwise aridification and climatic instability beginning at 3.6, 2.5 and 1.8 Ma, which are coincident with intervals of high diversity of savanna fauna such as bovids and hominids. These data tend to support suggestions that hominid evolution proceeded in mixed ecosystems, notably during periods of increased ecosystem variability.; This dissertation includes two chapters of material which have been previously published. Chapter II is from a forthcoming monograph edited by J. M. Harris and M. G. Leakey entitled Lothagam: Dawn of Humanity in East Africa (Harris & Leakey, in press). Chapter III has been published in the Journal of Human Evolution (Wynn, 2000). Chapters IV and V are in preparation for publication.